Suppression of Ammonia Volatilization from Rice-Wheat Rotation Fields Amended with Controlled-Release Urea and Urea

The critical period of ammonia volatilization (AV) is an important indicator in the development of control measures of AV. A field trial was performed for 2-yr with zero-N fertilization control (CK), controlled-release-urea (CRU), and urea in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) rotation system to investigate AV. The N application dosage was 255 and 225 kg N ha(-1) in rice and wheat season, respectively. The CRU was applied once as basal fertilization in each growing seasons. Urea was applied twice in the rice season, while it was applied three times in the wheat season. The results revealed that AV applied with urea was 61.4 and 57.3% higher than that with CRU in 2010-2011 and 2011-2012, respectively. The AV applied with CRU and urea predominately occurred at the rice flooding period, which accounted for 83.2 to 86.6% and 95.5 to 96.9% of AV at the entire rice season and for 48.2 to 49.6% and 67.2 to 70.4% of AV in the rice-wheat rotation period, respectively. No obvious difference was observed between urea and CRU treatments concerning grain yield, N concentration, and removal N of aboveground biomass. An obvious influence of rainfall on AV was documented because rainfall significantly reduced AV during the rice growth, while the rainfall before N fertilization could significantly increase AV in the wheat season. Therefore, the rainfall should be considered when applying N fertilizer, CRU should be recommended to use during the rice flooding period to decrease the AV rate.